Non-rupturing detonating cords



March 28, 1967 G. A. NODDIN 3,311,056

NON-RUPTURING DE TTTTTTTTTTT DS eeeeeeeeeeee bl INVEN (JEORGE A. Now/m TOR A] 1 ORNEY March 28, 1967 G. A. NODDIN 3,311,056

NON-RUPTURING DETONATING CORDS Filed March 22, 1965 2 Sheets-Sheet 2 EXPLOSIVE LEAD SHEATH POLYURETHANE ELASTOHER EXPLOSIVE LEAD SHEATH POLYUR NE ELASTO INVENTOR GEORGE A. NODDIN ATTORNEY United States Patent 3,311,056 NON -RUPTURING DETONATING CORDS George A. Noddin, Mantua, N.J., assignnr to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Mar. 22, 1965, Ser. No. 441,772 4 Claims. (Cl. 102-27) This invention relates to a product, and more particularly to non-rupturing detonating cords.

Detonating cords, i.e., articles comprising a core of detonating explosive usually surrounded by a metal sheath, e.g., of lead, or by fabrics or other conventional covering materials, have found wide use in the explosive arts as a means propagating a detonation from one point to another. One very large use of such products is in blasting. Detonating cords have also been used in metal forming and other metal working operations as well as for actuating mechanical devices. In recent years, detonating cords have found wide space-age application, e.g., in missle-stage separation. Though current devices have served well in the aforementioned applications, there has been an increasing need for detonating cords which are strong, light, tough and abrasion resistant yet do not release the products of detonation of the explosive contained therein. This invention provides such detonating cords.

The detonating cords provided by this invention are rapidly expanding and non-rupturing and comprise a core of detonating explosive surrounded by a sheath of elastomeric polyurethane. The sheath thickness increases With the explosive loading, with the particular core structure and, to a certain extent, with the explosive employed. Normally, the ratio of explosive loading, in grains/ft, to sheath thickness, in inches, is less than 130/ 1, and preferably from about /1 to 100/1.

In the attached drawings, FIGURES 1 and 2 illustrate schematically transverse and longitudinal cross-sections of one embodiment of cords of this invention.

FIGURES 3 and 4 illustrate schematically transverse and longitudinal cross-sections of an alternativeembodiment.

The polyurethane elastomers used in accordance with this invention are rubbery polymers having the recurring linkage Preferably, these polyurethanes contain polyester or polyether moities linked by moities derived from urethane contributing reactions usually isocyanates or amines. Examples of such polyurethanes are those described in US. Patent 2,929,802 formed by the'reaction of (1) a low molecular weight bis(chloroformate) and a diamine with (2) a bis(chloroformate) of a polyether glycol, preferably a polyalkylene ether glycol such as polyethylene ether glycol or polypropylene ether glycol. Other examples of polyurethanes are polyester urethanes such as those described in US. Patent 2,871,218 formed by reacting a polyester of an aliphatic dicarboxylic acid and an aliphatic glycol with a diphenyl diisocyanate, e.g., diphenylmethane diisocyanate, and free glycol, e.g., butane- 1,4-diol. Other examples of polyurethanes include arnide/ urethane/ether polymers such as those in US. Patent 2,- 929,801 formed by reacting monomeric diamine with an amide-forming derivative of a difunctional acid and a polyether bis(haloformate), particularly segmented polymers of high and low molecular weight constituents. Still other polyurethanes include chain-extended elastomers such as those shown in US. Patent 3,000,757 and US. Patent 3,100,721 formed by chain-extending polyesteror polyalkylene ether glycol-diisocyanate prepolymers with difunctional chain-extending agents including amines, glycols, etc., and particularly water or hydrazine. In addition to polyurethanes of the type described in the above patents which patents are incorporated herein by reference, other polyurethane elastomers useful in this invention include those of the types described in US. Patent 2,729,618 and US. Patent 3,012,992, each of which are also included herein by reference.

The explosives used in the cords of this invention can be any of the wide variety of explosives conventionally used in detonating cords. Chief among these are capsensitive organic nitrates, nitramines and nitro compounds as well as inorganic QZldES. Examples of such explosives are pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), cyclotetr-amethylenetetranitramine (HMX), tetryl, tetranitrodibenzotetraazapentylenes such as tetranitrodibenzo-l,3a,4,6a-tetraazapentylene, trinitrotoluene (TNT), lead styphnate, nitromannite, picryl sulfone, 'bis(trinitroethyl) urea or a mixture of one or more of the foregoing explosives. Explosives such as those just mentioned can be used alone or in combination with one or more additives, for example, powdered metals such as aluminum, magnesium, boron, titanium, zirconium, tellurium and selenium as well as mixtures of one or more of the foregoing metals; one or more inorganic oxidizing salts such as ammonium nitrate, sodium nitrate, red lead and alkali and alkaline-earth metal chlorates and perchlorates; and various binders for the explosive compositions such as natural and synthetic rubbers, e.g., butyl rubber, nitrocellulose and epoxy resins as well as plasticizers for such binders. A preferred multi-component core composition is the type of deformable, self-supporting composition used in sheet explosives. Of these, compositions of the type shown in US. Patent 2,992,087 containing, e.g., PETN, nitrocellulose and a trialkyl ester of Z-acetoxy-1,2,3-propanetircarboxylic acid and the compositions of US. Patent 2,999,743 containing e.g., PETN, butyl rubber and terpene resin, are particularly preferred.

In the products of this invention, the explosive core can be directly in contact with the elastome'ric polyurethane sheath. Alternately, the polyurethane sheath which surrounds the core can be in contact with a metal sheath which in turn is in contact with the explosive, core. For example, a piece of conventional detonating cord, either countered or uncountered, can be inserted within a polyurethane sheath. Thus, the products of this invention comprise a core of detonating explosive surrounded by a polyurethane elastomer sheath which can be directly in contact therewith or separated from the core by one or more layers, e.g., of metal such as lead or aluminum, plastic or fabric, as in the case, for example, where a conventional detonating cord is inserted in the sheath. Some applications require devices in which the detonation products are completely contained while others require only a degree of containment, so that the system is not exposed to detonation products such as gases and metal fragments. In the former case the polyurethane sheath completely encapsulates and covers the ends of the core, while in the latter case the explosive of the core may be exposed at one or both ends of the core. In"the case of complete confinement, preferably the initiation means, for example, a miniaturized blasting cap, may be inserted with the sheath adjacent the explosive of the core and the polyurethane sheath sealed around the device. In the case where the core is exposed, it is often convenient to attach a conventional initiator, such as an electric blasting cap, to the core in the arrangement in which the cords of this invention are employed. Usually, the amount of explosive and material surrounding the core is such the polyurethane sheath expands at least 25%, and preferably 50 to in diameter on detonation of the core as measured by a framing camera.

The amount of explosive employed depends on the amount of expansion of the cord, the strength of the detonation impulse desired, the explosive used, the degree of confinement of the core, and the structure of the sheath. Generally, the amount of explosive increases with the expansion and impulse and, for a given expansion, increases with number and thickness of the layer or layers of material surrounding the core. Usually, the loading of explosive, excluding additives such as metallic fuels, binders and plasticizers, ranges from 1 to 400, and preferably 2 to 100 grains per foot.

The non-rupturing cords of this invention can be pre pared, particularly in short lengths, by merely inserting a preformed core of explosive in a preformed tube of polyurethane. Alternately, and preferably for longer lengths, the polyurethane sheath can be continuously extruded around a preformed explosive core in a precentered die, e.g., such as that used in wire coating. A strip of polyurethane also can be wound around the core with overlapped edges securely sealed to prevent rupture of the polyurethane sheath on detonation of the core.

As indicated hereinbefore, the thickness of the elastomeric polyurethane sheath depends upon the expansion desired, the explosive charge, the degree of confinement of the core, and the interposed layers between the core and the sheath, but, in any case, should be sufficient to prevent rupturing of the sheath on detonation of the core. Usually, to prevent rupturing, the ratio of detonating explosive exclusive of additives, in grains per foot, to wall thickness, in inches, is less than 130/1 and preferably /1 to 100/1. If the core has a lead sheath, e.g., as in the case Where a conventional detonating cord is inserted in a polyurethane sheath, lower ratios, e.g., 50 grains per foot/inch or lower are normally employed. Where completely confined cords are employed, that is, where the polyurethane sheath surrounding the core also covers the ends of the core and the initiating means, it is also often desirable to use somewhat lower ratios of explosive loading to sheath thickness.

The products of this invention are characterized by the fact that they are rapidly expanding and non-rupturing, and are strong, lightweight, tough and abrasion resistant. Freedom from detonation products is particularly important in space-age uses where, for example, such products might follow an orbiting satellite obscuring or effecting the satellites data-gathering mission, or in any other use where released combustion products would have a deleterious effect. Since the cords do not rupture, danger from shrapnel from metal surrounding the core and danger from combustion heat and flame is eliminated. Thus, if temperature-sensitive materials are adajcent the cord, the risk of their decompositions is eliminated. The cords of this invention also greatly muffle the noise of detonation.

The cords of this invention can be used in those applications where detonating cords are used conventionally. In space applications, they find particular utility in separating metal parts, e.g., missile stages. In such application, the cord is usually juxtaposed a groove or other weakened area at the line of desired separation. Detonation of the core expands the sheath and separates the parts along a line adjacent the cord. The products find utility generally in any application where the environment through which the cord passes is sensitive to shocks, noise, combustion products or heat and flame.

In the following more specific examples which further illustrate this invention, parts and percentages are by weight unless otherwise indicated. In the following examples, polyurethane A was prepared -by reacting the following materials in the indicated ratio by the general procedures shown in the aforementioned patents: 1 mole of polytetramethyleneether glycol bis(chloroformate), 2 moles of 1,4-butanediol bis(chloroforrnate), 4 moles of piperazine and 1 mole of adipyl chloride. Polyurethane elastomer B was prepared from polytetramethyleneether Polyurethane Elastomcr Property AS'IM t Method A 13 C D Hardness, Shore A D676. 86 85 85 83 Stress-strain (room temp):

Mm, p s.i 875 905 740 975 Mm, D.S.i 1,125 1,330 1,220 c. M 00, p 51. D4412 1,450 1, 705 1. 800 1.900 T 1).S.i. 4, 800 4, 375 '1, 600 2,000 En, percent" 600 (V0 525 3-10 Sn, percent- 120 87 20 32 Compression set, pore W 29 28 4 22 hrs. at room temp 22 hrs/" o i' 3MB)- {60-70 47 as Split Tear, lh./linear in D470 120 121 143 I16 Yertlov Resilience, percent" D 345.-. 83 75 40 Low Temp. Brittle PL, F D440.-. 106 l60 ll0 02 NBS Abrasion, percent D394 300 693 245 In the table the modulus M is given in p.s.i., at the indicated elongations, for example, a stress of 875 p.s.i. gives an elongation of 100% for A. T is the tensile strength at break; E is elongation at break; and S is the tension set at break.

Examples 1 t0 5 Non-rupturing detonating cords are prepared by inserting the following cores in preformed sections of 0.130-inch I.D., 0.550-inch O.D. tubing of polyurethane elastomer A. To test the characteristics of the cords, a No. 6 blasting cap is attached to one end of each cord, extending beyond the end of the polyurethane sheath, then initiated in air. The results are:

Core

Example Result Weight of Composition Explosive (excluding additives), grains/it.

PETN A 17.5 Did not rupture.

PETN 20.0 Do.

PIEIN in .105 in. 0.1). 10 Do.

load sheath.

PEIN B 27 Ruptured in 1st trial. Did not rupture in 2nd trial.

5 PETN 37 Siieatnruptnred.

11 Self-supporting mixture of about of PETN and 15% of an equiweignt mixture of butyl rubber and terpene resin (1iccolyte S-lO and S40 grades).

The procedure described above can be repeated using an equivalent weight of RDX, HMX or tetranitrodibenzotetraazapentylene instead of PETN in the core to yield non-rupturing cords having properties similar to the above cords. Similarly, the sheath can be prepared from polyurethanes B, C or D to yield similar non-rupturing cords of this invention.

Example 6 A core of 5 grains per foot of the commercially known Pyrocore (60/40, lead azide/aluminum, lead jacketed with an OD. of 0.088 inch) is covered with a sheath of polyurethane A having a wall thickness of 0.25 inch. The polyurethane is disposed on the lead-covered core by extruding the polyurethane around the Pyrocore core in a precente-red-die extruder. Detonation of the lead azide mixture does not rupture the cord. If the polyurethane jacket is omitted, detonation of the lead azide mixture. completely consumes the cord and lead covering.

I claim:

1. Non-rupturing detonating cords comprising a core of cap-sensitive detonating high explosive and a sheath of polyurethane elastomer, the ratio of the amount of explosive in grains per foot to sheath thickness in inches being about from to 1 to 130 to 1.

2. A cord of claim 1 wherein said core consists essentially of 2 to 2 0 grains per foot of PETN in a lead sheath.

3. A cord of claim 1 wherein said core consists essentially of a mixture of PETN, butyl rubber and terpene resm.

4. A cord of claim 1 wherein said core consists essentially of a mixture of PETN, nitrocellulose and a trial-kyl ester of 2-acetoxy-1,2,3-propanetricarboxylic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,687,553

8/1954 Colombo 102-27 X 6 2,992,087 7/ 196-1 Fassnacht et a1. 10227 X 2,999,743 9/1961 B'reza et a1 102 27 X 3,129,663 4/1964 Schnepfe 1o2 X FOREIGN PATENTS 815,534 6/1959 Great Britain.

References Cited by the Applicant UNITED STATES PATENTS 2,863,353 12/ 1958 Brimley. 2,982,210 5/1961 Andrews et al. 2,993,236 7/ 196 1 Brimley et a1. 3,032.35 6 5/ 1962 Botsford.

BENJAMIN A. BORCHELT, Primary Examiner.

V. R. P-ENDEGRASS, Assistant Examiner. 

1. NON-RUPTURING DETONATING CORDS COMPRISING A CORE OF CAP-SENSITIVE DETONATING HIGH EXPLOSIVE AND A SHEATH OF POLYURETHANE ELASTOMER, THE RATIO OF THE AMOUNT OF EXPLOSIVE IN GRAINS PER FOOT TO SHEATH THICKNESS IN INCHES BEING ABOUT FROM 10 TO 130 TO
 1. 